Perovskite solar cells have shown remarkable progress in recent years with rapid increases in conversion efficiency, from initial reports of 2-3% in 2006 to 20% in 2015. Perovskite solar cells may offer the potential for an earth-abundant and low-energy-production solution to truly large-scale manufacturing of photovoltaic (PV) modules. While perovskite solar cells have achieved very high efficiencies in a very short amount of time, a number of challenges remain before perovskite solar cells can become a competitive commercial technology.
Although organic-inorganic perovskite materials have been studied for more than a century, initial studies on methylammonium lead halides for semiconductor applications, including thin-film transistors and light-emitting diodes, started in the last two decades. The first application of hybrid organic-inorganic perovskite absorbers in solar cells occurred in 2006. However, these early cells were of rather poor efficiency (<4%) due in part to the liquid electrolyte used, which limited both device stability and the open circuit voltage due to compromised interfacial chemistry and energetics. The application of a solid-state hole transport material (HTM), Spiro-MeOTAD (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene) improved the efficiency to 10% by 2012. Subsequent improvements in performance and stability have come through continued investigation of mixed halide perovskites, improved contact materials, new device architectures, and improved deposition processes, with 20% efficiency having been reported in late 2014. However, there remains a need for improved organic-inorganic perovskite compositions and materials to further improve the performances of devices fabricated from these materials so that they can successfully compete with incumbent materials, both from technical and economical perspectives.